Occultation Timing Activity

Timing asteroid occultations is a great activity for an amateur astronomer who wants to tackle serious research. Occultations are like tiny eclipses. Instead of the Moon and the Sun, it's an asteroid and a star, usually a faint star. Most occultations are very brief -- a few seconds. Most don't happen at all because our predictions aren't perfect yet. But they're getting better (see some here) and there's tremendous fun to be had if you're patient. I report my observations to the International Occultation Timing Association (IOTA).

There's an occultation coming up.  The dome is overflowing with karma!

Here's the star SAO 100819 in Bootes just as it was occulted by the asteroid Varsavia in 2003.  Dozens of amateur astronomers along the Pacific Coast observed this event.  Click on the picture for full details.

Occultations can be recorded by eye alone but a TV camera and VTR are better. This old RCA intensified camera can "see" stars fainter than I can. But it's a bit of a boat anchor. Boat anchor is ham slang for a heavy old radio that has seen better days. We need to know when the asteroid covers and uncovers the star. Timing these events to 0.1 second is our goal. You can use GPS for this, but then you need a hard-to-find accessory called a video inserter. It's more economical to use a shortwave receiver. The signal from WWV and/or WWVH (typ. 5 MHz) goes onto the VTR soundtrack while the camera is "looking" at the star being occulted. This Icom 735 (at left) is 1986 vintage and is the unit that I installed in my old gray car. My antenna is 20 feet of hookup wire attached to the tip of the mast in the top photo.

The microprocessors in the observatory cause "birdies" that interfere with WWV. The problem is worse at night when the propagation drops off. To suppress the birdies, I run RG-58 coax from my "rig" over to the slot under the dome where the wheels are. The coax plugs into a BNC jack mounted on the bent bar seen at left. Thus the coax is grounded to the dome via a wheel. The white antenna wire is passed under the dome and connected to the white binding post, which completes the circuit to the inner conductor of the coax. The improvement in quality when the coax is grounded in this manner is dramatic. The dome seems to act as a Faraday shield, bottling up the birdies. Rotating the dome has no effect on the received signal.